1. Field of the Invention
This invention pertains to an automatic transmission controller for powered vehicles and more particularly to electronic transmission control of a vehicle having a plurality of gears in the forward and reverse directions.
2. Description of the Prior Art
The trend in powered vehicles in recent years has been toward increased size and articulation of the vehicles. Reliable mechanical transmission shift linkages for such vehicles have become costly to design and build and require frequent adjustment and maintenance due to mechanical wear. Further, where such linkages are manually activated by the vehicle operator, potential damage to the transmission due to operator error increases with the size and complexity of the vehicle.
Electronic controls for generating transmission shift patterns are known in the prior art. A pertinent example is the U.S. Pat. No. 3,640,156 to Mori et al disclosing a control system which continuously monitors and uses signals indicative of: (1) speed selector lever position; (2) throttle valve setting; (3) engine intake manifold vacuum; (4) vehicle ground speed; (5) engine temperature; and (6) road grade. These signals are used to determine both upshifting and downshifting points.
U.S. Pat. No. 3,646,835 to Ito et al. discloses a shift control system using combined electrical and hydraulic controls. The gear shift point is determined by comparison of engine throttle opening and transmission output shaft speed (angular velocity), using discrimination circuits. The digital reading which represents the angular velocity of the output shaft is immediately converted to an analog signal for subsequent comparison purposes.
U.S. Pat. No. 3,702,572 to Wakamatsu et al discloses an automatic transmission control system which monitors throttle setting, vehicle speed and road grade to determine gear shift points. The driving signals are processed by analog circuitry until the gear shift decisions are made, after which digital logic circuitry and memory means are used to control the gear change solenoids.
U.S. Pat. No. 3,703,109 to Irie et al discloses an electronic transmission control device which effects smooth downshifting by determining a "neutral" interval (no upshift or downshift) in accordance with engine torque and vehicle speed. The Irie circuitry (all analog) derives a first voltage signal varying directly with engine torque and a second voltage signal varying inversely with vehicle speed; these signals are processed and combined by standard analog techniques.
The U.S. Pat. No. 3,732,755 to Beig et al. discloses an electronic transmission control system which monitors throttle setting, vehicle speed and gear select lever position. The signals are processed digitally and are combined to provide gear shift signals. A magnetic pickup device on the vehicle wheels provides a digital pulse count representing vehicle speed, and the interval over which such pulses are counted is determined by an analog voltage signal proportional to engine load.